A friction stir welding device (hereinafter, referred to as FSW (Friction Stir Welding) apparatus) is an apparatus which applies friction heat to a member to be welded by a rotating welding tool, causes a plastic flow phenomenon in the member to be welded, stirs the member to be welded by the welding tool, and welds the member to be welded. Herein, when the welding tool is continuously used to be in an overheated state, the welding tool is easily worn out or damaged. Regarding this problem, PTL 1 discloses in claim 1 that “ . . . includes a control device which controls at least one of a rotating speed of the welding tool driven by the tool rotating drive device and a moving speed of the welding tool driven by the tool moving drive device such that the tool temperature falls within a predetermined range of management temperature.”